Stimulation parameters setting: The first programming is performed at 3-4 weeks after surgery. Bilateral contacts are as cathode for monopolar configuration. The initial voltage, pulse width and frequency are bilaterally 1.0-1.5 V, 60 μs and 130 Hz for each individual, respectively. Voltage is gradually increased to a stable level first, until the optimal efficacy is achieved. Two weeks later, when patients came back to hospital for reprogramming, the voltage is also first adjusted to optimize the stimulation parameters. Either pulse width or frequency will be adjusted when increasing voltage more than 0.4 V for one time still can not get satisfactory outcomes. The frequency is adjusted when bilateral symptoms are unresponsive to voltage. Frequency is increased by 15-20 Hz for each time. Pulse width is then adjusted for the satisfactory clinical response of unilateral symptoms which are not satisfied after increasing voltage or frequency. Pulse width is increased to 90 μs if necessary (e.g. severe tremor).